1. Field of the Invention
The field of this invention lies within the field of dot matrix printers. More particularly, the field lies within the art of dot matrix printers which are characterized as line printers having a series of hammers that are released from a hammerbank. The hammerbank has permanent magnets for retention of the hammers, and electrical coils to overcome the magnetic retention by reversing the polarity for releasing the hammers. It particularly relates to that aspect of the magnetics which permanently retain the hammers and interact with adjacent magnetic forces including those of the pole pieces.
2. Prior Art
The prior art of line printers with permanent magnets incorporates numerous magnetic orientations. Oftentimes, these magnetic orientations are such where an elongated bar magnet is used to cause a pair of pole pieces to retract a hammerspring. The pole pieces are such wherein they receive a permanent magnet between them.
The pole pieces can be oriented so as to have shunts and air gaps for modifying the action of the permanent magnets. However, by in large, such permanent magnetism is provided by a magnet which is placed in a notch, space, or slot between pairs of pole pieces. The magnetism flows from the permanent magnet through the pair of pole pieces for retracting the hammer against the pole pieces.
Coils are wrapped around the pole pieces and overcome the permanent magnetism of the magnetic circuit so that a release of the sprung hammers of the hammerbank can be effected. This is when the permanent magnetism is counteracted so that the hammers are released and move away by their spring action from the ends of the pole pieces. During this release action, the permanent magnetism and the reverse flux provided by the coils creates a dynamic within the interaction of the hammers and the interfacing adjacent pole pieces. This interaction within the hammers is such that magnetic phenomena dynamically changes between the hammers, the pole pieces, and the magnetic circuit.
The dynamic interaction is extremely critical to the phases of printing. When the hammers are released, the relative phases of printing, as the hammers each respectively strike the print ribbon and the underlying media, can vary depending on the magnetic interaction between adjacent hammers and pole pieces. As can be appreciated, if the hammers are released too slowly, too quickly, or magnetically retracted in a particularly variable manner without consistency, the dots in a line matrix printing or other dot matrix printer are not accurate and do not present clear print. This is most critical with regard to such items today as bar codes that are printed onto an underlying media for bar code reading.
The position of a hammerspring in contact or when away from a pole piece affects the magnetics, and magnetic forces are imposed on the other hammerspring magnetic circuits. These interactive changes during the operation of the hammerspring is a major problem. When such interaction takes place, it tends to occlude and change the desired operating characteristics of the magnetics and attendant hammersprings. Such interaction, can create a cascading effect. The magnetic effects of one hammerspring and magnetic circuit of the pole pieces can be transferred to another one. Likewise, down the line of a plurality of hammersprings and magnetic pole pieces, a cascading effect is created in a line printer thereby affecting them on a cascading basis.
The foregoing cascading effect can vary depending upon the dynamics of operation. For instance, if one particular series of adjacent springs are releasing and retracting, they can effectively create a cascade effect in an adjacent relationship. To this extent, they can change the magnetic effects on a constantly shifting basis. As a consequence, if this problem can be resolved or reduced it is eminently helpful to the accuracy and functions of a printer, especially a printer printing bar codes.
When viewing the hammers and the pole pieces, it can be determined that permeance exists between them. In effect, the magnetic flux can transit or leap from one pole piece to a neighboring pole piece or pole pin. This permeance is inversely proportional to the distance between the pole pieces. In other words the farther they are away in spacing, the less the permeance and effect of mutual inductance has on the magnetic circuits. Further to this extent, the permeance is directly proportional to the adjacent or facing areas of neighboring pole pins or pole pieces. In other words, as the adjoining or adjacent area of the pole pieces increases, there is a directly proportional increase of magnetic permeance between the pole pieces or pins.
In order to overcome these deficiencies a decrease in the adjacent areas is utilized to resolve the problem. This is effected by removing a portion of the pole pieces or pole pins having areas in adjacent relationship to each other. By doing this, the characteristics of the permeance between the adjacent pole pieces is diminished. In effect, the connection of the magnetic flux of the permanent magnets to the pole pieces is diminished and more discrete and precise printing operations can be effected.
In order to provide for this decrease in permeance through reduced adjacent areas, the surface areas are diminished. Also the magnetics provided by the permanent magnet are split. The split magnet is interconnected by a keeper in order to provide for connected magnetic functions through the magnetic circuit.
The reduced permeance of the pole pieces to neighboring pole pieces results in reduced mutual and self inductance. Thus, the changes in forces on a hammerspring in the released and retracted positions or during the dynamic movement as well as in the static position upon return is reduced as to neighboring pole pieces.
The changes in dynamic magnetic pull back forces in the hammers and pole pieces because of the positions of neighboring hammersprings is one of the worst case conditions. This is particularly true when the hammerspring spacing between them is reduced which in turn creates greater permeance. To solve this, this invention specifically reduces the geometry of the pole pins as to their mutual facing areas, and reduces self and mutual inductance through the reduction of permeance. In this manner, faster circuits are achieved that are better matched for the timing and voltage levels to allow for less energy per stroke to be consumed from the power supply and more accurate printing. As a consequence, this invention is a broad step over the prior art by increasing speed and accuracy of printing as well as reducing the power requirements.